268 Capt. Lynes on the Ornithology [Ibis, 



Tliroughoufc the Middle-Atlas, the distinguished French 

 geologist, M. Gentil, has discovered evidences of much 

 Tertiary or " Recent " volcanic disturbance. 



My personal acquaintance with the Plateau showed that 

 its surface, at least as tar south as Timoudit and for many 

 miles around Jebel Hehljri, is composed almost entirely of 

 volcanic tufa and basalt; a vast, scarcely undulating flat, 

 broken only by sundry " Volcanic Kopjes "' and " C'raters," 

 the former chietly collected towards the northern edge. 



The " Volcanic Kopjes," of which Jebel Hebbri, standing 

 some 500 feet above Plateau level, is the largest, nre cones, 

 nearly flat-topped or with shallow imperfect craters. 



The " Craters " are without li]) or any sign of ejected 

 materials, and so, presumably, the result of subsidence ; their 

 sides, often very steep or even vertical, are of hard basalt of 

 columnar or trap formation ; some are as large as 500 yards 

 diameter at Plateau level, and 300 feet deep ; the smallest are 

 mere ''pot holes," 30 yds. X 20 feet {sic). 



Beyond Timoudit, whose fortress is perched on the summit 

 of a scoria-sided volcano which rises from an exposed 

 limestone base to about 500 feet above the valley of the 

 Ouad Guigoii, I did not go : but viewed from the fortress, 

 it was clear from the appearance of its northern face that 

 that part of the main chain of the Middle-Atlas is largely 

 composed of limestone, and lacks the volcanic elements of 

 the Plateau, except, ])erhaps, just where its base meets the 

 Plateau. 



Two other niinor features worthy of note in the Pange are, 

 (a) the "Mamelons^' in the Tigrigra Valley at the base of 

 the llange, {It) the "' Terrace " on its North Slope. 



The " Mamelons '" are a number of separate little hills up 

 to 500 feet high, of two ty[)es : the " mound," an unbroken 

 rounded luunniock like an apple-pudding, and the *' rocky,^' 

 surmounted _ by small crags, dropping in screes on the 

 north and west faces down to their b;ises ; some abut so 

 intimately on the " North Slope " as almost to form a spur, 

 others stand clear on the floor of the valley (see Plate Wl.h). 



They seem to be formed of Priuiary rocks, slates, and 

 scliists ; but 1 can advance no theory as to their origin. 



